<p>Urban forests have high conservation value and provide recreational benefits. Riparian forest remnants have high ecological importance but are negatively impacted in urban areas. Subsidies (i.e., allochthonous inputs of resource and nutrient from outside the ecosystem) play important roles in this ecosystem and can be altered by anthropogenic activities leading to changes in ground arthropod communities and leaf litter decomposition. To test the role of subsidy impacts in this ecosystem (i.e., urban grass dumping), we designed a blocked factorial litter manipulation experiment. Treatments included a control, litter removal, litter addition, and urban grass addition. We measured rates of decomposition of native red oak and sugar maple leaf litter, and ground arthropod abundance and composition. Ground arthropod abundance was significantly affected by the treatment, mainly due to its effect on springtails, which were less abundant in the litter removal plots and more abundant in the grass addition plots. Treatment did not affect the abundance of spiders, beetles, or ants and other arthropod groups. We found significant differences in community composition between the litter removal and other treatments. Litter removal and grass addition significantly increased decomposition rates of native red oak and sugar maple leaves. We have shown that anthropogenic subsidies can impact arthropod communities and native leaf litter decomposition. This increases our understanding of how ecosystems are impacted by anthropogenic subsidies and other resource manipulations and could further the conservation value of urban riparian forests.</p>